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B. STRATIFIED EPITHELIAL. This type of epithelium has more than one layer of cells present. The epithelium is named according to the shape of the surface cells even though the underlying cells may be a different shape. For example, if the surface cells are squamous, but the underlying cells are cuboidal or columnar, the epithelium is a stratified squamous epithelium.

1. Stratified squamous, noncornified (moist).

a. On slide 131, Esophagus (H&E) identify the noncornified, stratified squamous epithelium. Note the flattened, nucleated surface cells, the “middle zone” of the polyhedral shaped cells, and the basal layer of the polyhedral shaped cells, and the basal layer of columnar cells which rests on the basement membrane. Characteristically, the lower surface of the epithelium is undulated.

2. Stratified squamous, cornified (dry). Slide 4, Thin skin (H&E) and Slide 46, Thick skin (H&E). Study the representative types of cornified, stratified squamous epithelial. Note the characteristics of the cells at the various levels. The surface layer of cells, represented by the stratum corneum of the epidermis, lacks nuclei and keratin proteins have replaced the cytoplasm. The surface cells of the skin are constantly desquamated. They are replenished by mitotic divisions occurring in the basal layer of epithelial cells. Note how much thicker the stratum corneum is for thick skin than for thin skin.

3. Stratified cuboidal and stratified columnar. On slide 111, Epiglottis (H&E) look in the connective tissue underlying the surface epithelium for ducts of glands lined with stratified cuboidal or stratified columnar epithelium. The surface epithelium of the epiglottis is an intermediate type where a change is being made from stratified squamous to pseudostratified columnar. (Some of the surface cells are torn off.)

4. Transitional epithelium of the urinary passages and bladder shows variations in thickness according to the contracted or dilated state of the structure this epithelium lines. For example, in the contracted urinary bladder, the epithelium may be five or six cell layers thick with the surface cells appearing as large, cuboidal cells that bulge into the lumen. The basal cells are smaller than the surface cells and they interdigitate with the overlying cells. When the bladder fills with urine and becomes distended, the epithelium appears to be only two or three layers thick, and the surface cells are flattened.

a. On slide 121, Urinary bladder (H&E), identify the transitional epithelium and study its characteristics. Are any of the surface cells binucleated?